With a piston of the type which comprises a cylindrical steel core, for example of disc form, connected with a piston rod and, fitted to this core, a sealing ring with sealing lips, formed integrally of rubber or a plastics material similar to rubber having good sealing properties, it is not only necessary to ensure that the piston is accurately controlled during its reciprocal movements inside a cylinder but it must also be ensured that a reliable seal is provided between the piston and the cylinder walls which guide the piston, because the chambers on either side of the piston must be well sealed against each other. Known assemblies which are comparable to the above fail to provide an optimum solution of the problem and are moreover relatively expensive.
According to the present invention there is provided a piston especially for pneumatic cylinders, comprising a rigid core connectable with a piston rod, a sealing ring mounted on the core and having integrally formed sealing lips, the sealing ring being formed of rubber or a plastics material having sealing properties similar to rubber, and a guide ring which is fitted around the sealing ring and is formed of a slideable plastics material to be axially fixed and radially resilient relative to the core.
Preferably the guide ring is slotted and the cross-section of the guide ring is of the shape of a letter C turned into a horizontal position. Preferably also the sealing ring has a circumferential surface and a transverse member of the guide ring extends parallel to the circumferential surface, two legs, of the guide ring embracing the circumferential surface of the sealing ring from opposite sides. It is particularly advantageous that the guide ring is formed of a graphite-filled plastics material, preferably of the polyamide group.
Further the core may have a plurality of cut-outs which are uniformly arranged around the circumference of the core, are of a substantially arcuate contour, and open externally so that the material of the sealing ring may engage with the core from externally. The circumference of the core may be completely covered by the material of the sealing ring, the thickness of the covering being greater in the regions of the cut-outs than in the regions therebetween.